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Spark ignition System. Primary Ignition Circuit(low voltage) Battery Ignition switch Primary windings of coil Contact breaker capacitor Secondary Ignition Circuit ( high voltage) Secondary windings of coil Distributor cap and rotor (if the vehicle is so equipped) Spark plug wires
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Primary Ignition Circuit(low voltage) • Battery • Ignition switch • Primary windings of coil • Contact breaker • capacitor • Secondary Ignition Circuit ( high voltage) • Secondary windings of coil • Distributor cap and rotor (if the vehicle is so equipped) • Spark plug wires • Spark plugs
Ignition System Operation • The ignition system includes components and wiring necessary to create and distribute a high voltage (up to 40,000 volts or more). • All ignition systems apply voltage close to battery voltage to the positive side of the ignition coil and pulse the negative side to ground. • When the coil negative lead is grounded, the primary (low-voltage) circuit of the coil is complete and a magnetic field is created by the coil windings.
Ignition System Operation (continued) • When the circuit is opened(by contact), the magnetic field collapses and induces a high-voltage spark from the secondary winding of the ignition coil. • Distributor ignition (DI) is the term specified by the Society of Automotive Engineers (SAE) for an ignition. Get that spark and distribute to spark plug
ELECTROCHEMICAL CELL BASICS • Pbo2 + Pb - • Four Basic • Components • Positive Electrode • Negative Electrode • Separator • Electrolyte
A car battery is a type of rechargeable battery that supplies electric energy to an auto mobile Usually this refers to an SLI battery (starting, lighting, ignition) to power the starter motor, the lights, and the ignition system of a vehicle’s engine. This also may describe a traction battery used for the main power source of an electric vehicle
Automotive starter batteries (usually of lead acid type) provide a nominal 12-V by connecting six galvanic cell in series. Each cell provides 2.1 volts for a total of 12.6 volt at full charge. Lead-acid batteries are made up of plates of lead and separate plates of leaddioxide which are submerged into an electrolyte solution of about 35% sulfuric acid and 65% water This causes a chemical reaction that releases electrons , allowing them to flow through conductors to produce electricity . As the battery discharge, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate . When the battery is recharged , the chemical reaction is reversed: the lead sulfate reforms into lead oxide and lead. With the plates restored to their original condition, the process may now be repeated.
Ignition Coils • The coil creates a high-voltage spark by electromagnetic induction. • Many ignition coils contain two separate but electrically connected windings of copper wire. • Other coils are true transformers in which the primary and secondary windings are not electrically connected • The center of an ignition coil contains a core of laminated soft iron (thin strips of soft iron).
Ignition Coils (continued) • This core increases the magnetic strength of the coil. • Surrounding the laminated core are approximately 20,000 turns of fine wire (approximately 42 gauge). • These windings are called the secondary coil windings. • Surrounding the secondary windings are approximately 150 turns of heavy wire (approximately 21 gauge). • These windings are called the primary coil windings.
Ignition Coils (continued) • The secondary winding has about 100 times the number of turns of the primary winding, referred to as the turn ratio (approximately 100:1). • The primary windings of the coil extend through the case of the coil and are labeled as positive and negative. • The positive terminal of the coil attaches to the ignition switch, which supplies current from the positive battery terminal. • The negative terminal is attached to an electronic ignition module (or igniter), which opens and closes the primary ignition circuit by opening or closing the ground return path of the circuit.
How Ignition Coils Create 40,000 Volts • If the primary circuit is completed, current (approximately 2 to 6 A) can flow through the primary coil windings. • This flow creates a strong magnetic field inside the coil. • When the primary coil winding ground return path connection is opened, the magnetic field collapses and induces a voltage of from 250 to 400 volts in the primary winding of the coil and a high-voltage (20,000 to 40,000 volts) low-amperage (20 to 80 am) current in the secondary coil windings. • This high-voltage pulse flows through the coil wire (if the vehicle is so equipped), distributor cap, rotor, and spark plug wires to the spark plugs
The distributor handles several jobs. Its first job is to distribute the high voltage from the coil to the correct cylinder. This is done by the cap and rotor. The coil is connected to the rotor, which spins inside the cap. The rotor spins past a series of contacts, one contact per cylinder. As the tip of the rotor passes each contact, a high-voltage pulse comes from the coil. The pulse arcs across the small gap between the rotor and the contact (they don't actually touch) and then continues down the spark-plug wire to the spark plug on the appropriate cylinder. When you do a tune-up, one of the things you replace on your engine is the cap and rotor -- these eventually wear out because of the arcing. Also, the spark-plug wires eventually wear out and lose some of their electrical insulation. This can be the cause of some very mysterious engine problems.
A cam in the center of the distributor pushes a lever connected to one of the points. Whenever the cam pushes the lever, it opens the points. This causes the coil to suddenly lose its ground, generating a high-voltage pulse. The points also control the timing of the spark. They may have a vacuum advance or a centrifugal advance. These mechanisms advance the timing in proportion to engine load or engine speed. Spark timing is so critical to an engine's performance that most cars don't use points. Instead, they use a sensor that tells the engine control unit (ECU) the exact position of the pistons. The engine computer then controls a transistor that opens and closes the current to the coil.
Spark plug construction • Terminal • The top of the spark plug contains a terminal to connect to the ignition system. The exact terminal construction varies depending on the use of the spark plug. Most passenger car spark plug wires snap onto the terminal of the plug, but some wires have spade connectors which are fastened onto the plug under a nut. Plugs which are used for these applications often have the end of the terminal serve a double purpose as the nut on a thin threaded shaft so that they can be used for either type of connection. These are a necessary part of the spark plug.
Insulator The main part of the insulator is made from porcelain. Its major function is to provide mechanical support for the centre electrode, whilst insulating the high voltage. It has a secondary role, particularly in modern engines with deeply inaccessible plugs, in extending the terminal above the cylinder head so as to make it more readily accessible. Ribs By lengthening the surface between the high voltage terminal and the grounded metal case of the spark plug, the physical shape of the ribs functions to improve the electrical insulation and prevent electrical energy from leaking along the insulator surface from the terminal to the metal case. The disrupted and longer path makes the electricity encounter more resistance along the surface of the spark plug even in the presence of dirt and moisture. A few spark plugs have insulators that aren't ribbed, but this is rare
Seals Because the spark plug also seals the combustion chamber or the engine when installed, the seals ensure there is no leakage from the combustion chamber. The seal is typically made by the use of a multi-layer braze because there are no braze compositions that will wet both the ceramic and metal case and therefore intermediary alloys are required. Metal case The metal case (or the "jacket" as many people call it) of the spark plug bears the torque of tightening the plug, serves to remove heat from the insulator and pass it on to the cylinder head, and acts as the ground for the sparks passing through the center electrode to the side electrode. As it acts as the ground, it can be harmful if touched while igniting. Center electrode The center electrode is connected to the terminal through an internal wire and commonly a ceramic series resistance to reduce emission of radio noise from the sparking. The tip can be made of a combination of copper. nicle. iron , or precious metal. In the late seventies, the development of engines reached a stage where the ‘heat range’ of conventional spark plugs with solid nickel alloy centre electrodes was unable to cope with their demands. A plug that was ‘cold’ enough to cope with the demands of high speed driving would not be able to burn off the carbon deposits caused by stop-start urban conditions, and would foul in these conditions, making the engine misfire. Similarly, a plug that was ‘hot’ enough to run smoothly in town, could actually melt when called upon to cope with extended high speed running on motorways, causing serious damage to the engine.
The answer to this problem, devised by the spark plug manufacturers, was a centre electrode that carried the heat of combustion away from the tip more effectively than was possible with a solid nickel alloy. Copper was the material chosen for the task and a method for manufacturing the Copper cored center electrode was created by Floform The center electrode is usually the one designed to eject the electrons (the cathode) because it is the hottest (normally) part of the plug; it is easier to emit electrons from a hot surface, because of the same physical laws that increase emissions of vapor from hot surfaces (see thermionic emission). In addition, electrons are emitted where the electrical field strength is greatest; this is from wherever the radius of curvature of the surface is smallest, i.e. from a sharp point or edge rather than a flat surface (see corona discharge). It would be easiest to pull electrons from a pointed electrode but a pointed electrode would erode after only a few seconds. Instead, the electrons emit from the sharp edges of the end of the electrode; as these edges erode, the spark becomes weaker and less reliable
Side electrode, or ground electrode The side electrode is made from high nickel steel and is welded to the side of the metal case. The side electrode also runs very hot, especially on projected nose plugs. Some designs have provided a copper core to this electrode, so as to increase heat conduction. Multiple side electrodes may also be used, so that they don't overlap the center electrode.
Spark plug gap Spark plugs are typically designed to have a spark gap which can be adjusted by the technician installing the spark plug, by the simple method of bending the ground electrode slightly to bring it closer to or further from the center electrode. The belief that plugs are properly gapped as delivered in their box from the factory is only partially true, as proven by the fact that the same plug may be specified for several different engines, requiring a different gap for each. Spark plugs in automobiles generally have a gap between 0.045"-0.070" (1.2-1.8mm). But it can depend on the engine: new spark plugs might be pre-gapped for a V-8 engine, installing all 8 plugs unchanged; however if installed in a 6-cylinder engine, all (6) plugs would require re-gapping .
Narrow-gap risk: spark might be too weak/small to ignite fuel; • Narrow-gap benefit: plug always fires on each cycle; • Wide-gap risk: plug might not fire, or miss at high speeds; • Wide-gap benefit: spark is strong for a clean burn. Gap gauge: A disk with sloping edge; the edge is thicker going counter-clockwise, and a spark plug will be hooked along the edge to check the gap
A spark plug gap gauge is a disc with a sloping edge, or with round wires of precise diameters, and is used to measure the gap; use of a feeler gauge with flat blades instead of round wires, as is used on distributor points or valve lash, will give erroneous results, due to the shape of spark plug electrodes. The simplest gauges are a collection of keys of various thicknesses which match the desired gaps and the gap is adjusted until the key fits snugly. With current engine technology, universally incorporating solid state ignitions and computerized fuel injection, the gaps used are much larger than in the era of carburetors and breaker point distributors, to the extent that spark plug gauges from that era are much too small for measuring the gaps of current cars.
Ignition Timing • Ignition timing refers to when the spark plug fires in relation to piston position. • The ignition in the cylinder takes a certain amount of time usually 30 ms (3/1000 of a second). • For maximum efficiency from the expanding gases inside the combustion chamber, the burning of the air-fuel mixture should end by about 10° after top dead center. Engine manufacturers include timing marks on their engines, so that the technician can check and adjust the engine timing if some conditions have changed.
Ignition Timing (continued) • If the burning of the mixture is still occurring after that point, the expanding gases do not exert much force on the piston because it is moving away from the gases. • Therefore, to achieve the goal of having the air-fuel mixture by completely burned by the time the piston reaches 10° after top dead center (ATDC), the spark must be advanced (occur sooner) as the engine speed increases.
Checking For Spark • If the engine is equipped with a separate ignition coil, remove the coil wire from the center of the distributor cap, install a spark tester, and crank the engine. • A good coil and ignition system should produce a blue spark at the spark tester.
Checking For Spark (continued) • Typical causes of a no-spark (intermittent spark) condition include the following: • Weak ignition coil • Low or no voltage to the primary (positive) side of the coil • High resistance or open coil wire, or spark plug wire • Negative side of the coil not being pulsed by the ignition module • Defective pickup coil • Defective module
